Wavelength division multiplexed (WDM) optical communication systems are known in which multiple optical signals or channels, each having a different wavelength, are combined onto an optical fiber. Such systems typically include a laser associated with each wavelength, a modulator configured to modulate the optical signal output from the laser, and an optical combiner to combine each of the modulated optical signals. Such components are typically provided at a transmit end of the WDM optical communication system to transmit the optical signals onto the optical fiber. At a receive end of the WDM optical communication system, the optical signals are often separated and converted to corresponding electrical signals that are then processed further.
Known WDM optical communication systems are capable of multiplexing 40 channels at 100 GHz spacing or 80 channels at 50 GHz spacing. These WDM optical communication systems occupy an overall bandwidth of 4000 GHz. At 50 GHz channel spacing and 100 GHz channel spacing, the occupied optical fiber bandwidth or spectrum is not efficiently used. As rapid growth of the Internet continues, and new applications arise, there is an increasing demand for higher data rates provided by underlying networks, which may be supported by advances in optical communication systems. Due to the increased demand, the information carrying capacity of an optical fiber preferably should also increase. As used herein, the terms “carrier”, “channel”, and “optical signal” may be used interchangeably.
One method to increase the data capacity of the occupied optical fiber bandwidth is to employ higher data rate modulation formats to modulate the optical signals or channels to carry data at higher rates. Such higher rate modulation formats, however, are typically more susceptible to noise, and, therefore, may not be used in transmission of optical signals over relatively long distances. Thus, the modulation format must be chosen according to a desired reach, or distance, the transmitted channels are expected to span. Other known systems, commonly called dense wavelength-division multiplexing systems (DWDM), are capable of packing even more densely, additional channels on an optical fiber by more closely spacing the channels together, such as at 25 GHz spacing between channels. While 25 GHz channel spacing is an improvement over 50 GHz and 100 GHz spacing, further improvement is still needed to meet the demands of increased data rates. However, the dense packing of individual channels at a reduced spectral spacing between channels has lead to challenges in reliably separating the individual channels at a receive end and increases error rates for the channel due to cross-talk between the adjacent channels or cross-phase modulation effects, for example. Thus, there is a tradeoff between optical communication system performance and the number of channels to be transmitted per fiber and their spectral spacing, as well as the modulation performed on each of the channels. Accordingly, for a specific embodiment, a maximum capacity can be achieved by optimizing the above parameters, such as the chosen modulation format for the optical signal, the span of the signal and the channel spacing between adjacent signals.
Preferably, the information carrying capacity of an optical communication system should be optimized to carry a maximum amount of data over a maximum length of optical fiber. For example, individual carrier or channel spacing should be minimized according to the available technology capable of reliably transmitting and receiving such minimally spaced channels. Therefore, a greater number of channels can be packed in a given bandwidth, resulting in more efficient use of network resources and the occupied optical spectrum of the channels. Additionally, when selecting the parameters and their respective values for optimizing the optical communication system capacity, the underlying network architecture should be considered as well as the data demands of the customer.
Accordingly, increased data demands of the network drive a need to provide a plurality of minimally spaced carriers to increase optical communication system network capacity. Additionally, unique customer requirements provide a need to flexibly group the plurality of minimally spaced carriers together in blocks or “superchannels” that can be individually routed throughout the network and that can be multiplexed with other blocks of similar minimally spaced carriers. Some known systems include routers or multiplexers with limited data capacity throughput. Thus, while optimum capacity of the optical communication system is generally desired, it is also preferred that the system capacity at any network component is not exceeded. Thus, it may be advantageous to limit the maximum data capacity available on each superchannel. In such cases when the data capacity is limited, it is preferred that the occupied bandwidth of the superchannel is minimized to obtain maximum spectral efficiency of the occupied bandwidth of an optical communication system.